This invention relates to wellhead systems and is specifically directed to seal assemblies, often referred to as pack-off assemblies, for sealing the annular space, referred to as an annulus or gland, between a wellhead casing hanger and the surrounding cylindrical wall of a wellhead.
This invention is specifically directed to a new and improved pack-off for such pack-off assemblies.
The U.S. Pat. No. 3,468,558 which issued as early as 1969, and later patents such as U.S. Pat. No. 3,871,449, explain the operation and purpose of pack-off assemblies as well as the various ways of running and setting the pack-off, i.e., sealing the annulus.
These patents also show different types of pack-offs for these pack-off assemblies and more recently the U.S. Pat. Nos. 3,797,864 of Hines and Ortolon and 4,521,040 of Slyker and Pettit illustrate more recent pack-offs. These latter patents show a pack-off comprising an elastomeric ring interposed between two metallic seal rings with each metallic seal ring having a pair of lips extending toward the elastomeric material which form a seal of elastomeric material and metal when the pack-off is set.
Attention is also directed to the U.S. Pat. No. 4,324,422 of Rains and Reimert in which a pair of metallic rings with dog-like overlapping fingers were embedded in elastomeric material and arranaged in a lost motion connection between the fingers. The lost motion connection allowed deformation of the elastomeric material when the pack-off was set and provided the pack-off with retrievable characteristics.
Still another pack-off which is part of the prior art is one utilizing upper and lower metallic rings with a deformable metallic band therebetween and surrounded by a plurality of elastomeric rings. The deformable metallic band is in the form of a plurality of V's laid sidewards having the elastomeric rings at the apex of the V's. When set, the end of the legs and apices of the V's, together with the elastomeric rings, engage the sidewalls of the annulus to form a seal. This type of seal needs a high amount of force to set and was also known to be used in a cylindrical annulus without an abutment to assist in expanding the metallic band and elastomeric rings. Retrieval of the pack-off was virtually impossible and the pack-off was usually destroyed when retrieval was attempted.
Another pack-off having retrievable characteristics is that shown in the U.S. Pat. No. 3,561,527 of Nelson which has a centrally located vertically oriented serpentine shaped band embedded in elastomeric material. The size and thickness of the serpentine band, like the pack-off of the U.S. Pat. No. 4,324,422 of Rains and Reimert, supra, interfered with the deformation characteristics of the elastomeric material and reduced the sealing capabilities of the pack-off.
It is therefore an object of this invention to provide a pack-off with metallic ring seals together with a serpentine band integral therewith with elastomeric material imposed therebetween and which is tapered to interface with a tapered annulus in a wellhead system.
The Related Applications, supra, discloses a wellhead system with a tapered annulus, and an abutment against which the tapered pack-off engages to expand and compress the pack-off for sealing the annulus. These applications also show various means for shifting the pack-off into the annulus. It will be apparent to those skilled in the art that the pack-off of this invention is capable of being used in the wellhead systems of these applications as well as any other wellhead system which has a tapered annulus and an abutment with any means for shifting the pack-off into the annulus such as those shown in any of the prior art patents, supra.